1. Field of the Invention
Aspects of the present invention relate to a rechargeable lithium battery.
2. Description of the Related Art
Lithium rechargeable batteries have recently drawn attention as a power sources for small portable electronic devices. Lithium batteries use an organic electrolyte solution, and thereby have twice the discharge voltage of a conventional battery using an alkali aqueous solution, and accordingly, have higher energy densities.
For a positive active material of a rechargeable lithium battery, lithium-transition element composite oxides capable of intercalating lithium, such as, LiCoO2, LiMn2O4, LiNiO2, LiNi1−xCoxO2 (0<x<1), and the like, have been researched.
For a negative active material of a rechargeable lithium battery, various carbon-based materials, such as, artificial graphite, natural graphite, and hard carbon have been used, which can all intercalate and deintercalate lithium ions. The graphite of the carbon-based material increases a discharge voltage and an energy density of a battery, due to a low discharge potential of −0.2V, as compared to lithium. A battery using graphite as a negative active material has a high average discharge potential of 3.6V and an excellent energy density. Furthermore, graphite is the most comprehensively used among the aforementioned carbon-based materials, since graphite guarantees a better cycle life for a battery, due to its outstanding reversibility. However, a graphite active material has a low density, and consequently, a low capacity in terms of energy density per unit volume when used as a negative active material. Further, there are some dangers, such as, explosion and/or combustion, when a battery is misused, overcharged, or the like, because graphite is likely to react with an organic electrolyte at high discharge voltages.
In order to solve these problems, a great deal of research on oxide negative materials for electrodes has recently been performed. For example, an amorphous tin oxide, developed by Japan Fuji Film Co., Ltd., has a high capacity per weight (800 mAh/g). However, the tin oxide has some critical defects, such as, a high initial irreversible capacity of up to 50%. The discharge potential of the tin oxide is more than 0.5V, and the tin oxide shows a smooth voltage profile, which is unique to the amorphous phase. Consequently, it was hard to develop a tin oxide applicable to a battery. Furthermore, a portion of the tin oxide was reduced to tin, during the charge and/or discharge reactions, which is a disadvantage for use in a battery.
Referring to another oxide negative electrode, a negative active material of LiaMgbVOc (0.05≦a≦3, 0.12≦b≦2, 2≦2c-a-2b≦5) is disclosed in Japanese Patent Publication 2002-216753. The characteristics of a rechargeable lithium battery including Li1.1V0.9O2 were also presented in the 2002 Japanese Battery Conference (Preview No. 3B05).
A negative active material of a metal vanadium oxide not including Li (i.e., x=0), as disclosed in Solid State Ionics, 139, 57-65, 2001 and the Journal of Power Source, 81-82, 651-655, 1999, has a different crystalline structure from a negative active material as taught herein. In addition, since negative active material of the references has an average discharge potential of more than 1.0 V, it may have problems when used as a negative electrode.
The above oxide negative electrodes do not show sufficient battery performance, and therefore, there has been a great deal of further research into oxide negative materials.